Hyperpycnal plume-derived fans in the Santa Barbara Channel, California

Hyperpycnal gravity currents rapidly transport sediment across shore from rivers to the continental shelf and deep sea. Although these geophysical processes are important sediment dispersal mechanisms, few distinct geomorphic features on the continental shelf can be attributed to hyperpycnal flows. Here we provide evidence of large depositional features derived from hyperpycnal plumes on the continental shelf of the northern Santa Barbara Channel, California, from the combination of new sonar, lidar, and seismic reflection data. These data reveal lobate fans directly offshore of the mouths of several watersheds known to produce hyperpycnal concentrations of suspended sediment. The fans occur on an upwardly concave section of the shelf where slopes decrease from 0.04 to 0.01, and the location of these fans is consistent with wave- and auto-suspending sediment gravity current theories. Thus, we provide the first documentation that the morphology of sediment deposits on the continental shelf can be dictated by river-generated hyperpycnal flows.